The father-of-one was the first officer to enter the premises, along with a highway patrolman who was passing by.

After hearing gunshots inside the bar, the pair entered the venue but Sgt Helus was immediately hit with a hail of bullets.

The patrolman dragged his injured colleague out, but he died the following morning in a Californian hospital.

Ventura County sheriff Geoff Dean paid tribute to his fallen co-worker and close friend during an emotional media conference following the attack.

He said the death toll may have been even higher were it not for Sgt Helus' bravery.

Undated photo of Sheriff's Sgt. Ron Helus, who was killed on Wednesday, November 7, 2018, in a deadly shooting at a country music bar in Thousand Oaks, California. Picture: Ventura County Sheriff's Department via AP

"Sgt Helus was having a conversation with his wife, as he does several times during the shift, and said to her, 'Hey I've got to go and handle a call, I love you'," he said, according to The Mirror.

"He died a hero. He went in to save lives, to save other people.

"Ron was a hardworking, dedicated sheriff's sergeant who was totally committed and tonight, as I told his wife, he died a hero because he went in to save lives."